German Patent No. 20 49 262 describes a traction control device for a motor vehicle, where the braking pressure on a driving wheel is increased by an anti-lock device when this wheel tends to spin, thus reducing the tendency to spin and allowing the vehicle to start moving. To increase the pressure, the driver is expected to actuate the brake pedal, so that the braking pressure built up by the driver is used for increasing the wheel brake pressure via appropriate control of a valve arrangement. In addition, this traction control is intended to be performed only if a switch that closes when the accelerator is depressed has been actuated.
If such a traction control is active, the braking action cannot be built up immediately if the driver suddenly wishes to brake, since the connection between the main brake cylinders, i.e., the service brake valve, and the wheel brakes of the unregulated wheels must be blocked.